JPH01201977A - Semiconductor laser device - Google Patents

Abstract

PURPOSE:To shift the phase of light propagating within laser in reference to diffraction grid and to simplify adjustment of amount of phase shift by bending stripe structure which forms laser. CONSTITUTION:After coating the entire surface of an n-type InP substrate 1 with resist, primary diffraction grid pattern is marked using HeCd laser beam, chemical etching is performed, and then a diffraction grid 5 is formed. An n-InGaAsP layer 2, an InGaAsP active layer 3, and then an InGaAsP buffer layer 4 are lamination-formed on this substrate 1 in sequence. Then, after performing patterning using a mask of bent pattern, mesa etching is performed to obtain a stripe with bent part at the center. Then, an InP layer 11 is allowed to grow again and an InGaAsP layer 6 is laminated on it. Then, an SiO2 layer 7 with a window is built up and a diffusion region 10 is formed by diffusing Zn so that it reaches the InP layer 11. After that, electrodes 8 and 9 are deposited, is turned into alloy, is divided into chips by cleavage, and SiN is built up on the cleavage surface. It allows a phase shift type DFB laser to be produced easily without using a complex resist coating process.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a semiconductor laser device, and particularly to a semiconductor laser device in which a grating is provided within or on a waveguide to stabilize the oscillation wavelength.

[Conventional technology]

Conventionally, in order to stabilize the wavelength of a semiconductor laser, a distributed feedback type (distributed feedback type) structure was used in which a grating was formed within the waveguide forming the semiconductor laser or in a portion close to the waveguide, and only a specific wavelength was reflected. DFB: Di
Semiconductor lasers (tributad feed back) have been proposed and prototyped.

In long-distance, large-capacity optical fiber communication systems, D
The performance required of an FB laser is that the secondary mode is sufficiently suppressed even during high-speed modulation, and stable single-longitudinal mode oscillation is achieved. The stability of single longitudinal mode oscillation is determined by the oscillation threshold gain difference between the major and minor modes. DF
The B laser has a high oscillation threshold gain difference due to the wavelength selectivity of the grating, but the phase shift type D laser was devised to have an even larger oscillation threshold gain difference.
It is an FB laser, and theoretically it is an input/4 shift type DFB.
Lasers are known to have the highest oscillation threshold gain difference, and development is progressing.

Conventionally, a common method for constructing a phase-shifted DFB laser has been to shift the phase of a grating midway. To form a diffraction grating with a phase shift in the middle of a laser structure, a phase shift film is formed in a pattern on a photoresist coated on a laser substrate, and then interference exposure is performed using laser light. I was worried. Further, the amount of phase shift was adjusted by changing the thickness of the phase shift film.

Furthermore, attempts have been made to form the diffraction grating uniformly and to shift the phase of the diffraction grating isometrically by shifting the phase of the light propagating in the laser or the waveguide forming the structure. As a method of shifting the phase of propagating light, attempts have been made to widen the shape of the waveguide, for example, the width of a stripe in a portion, and delay the phase in that portion.

[Problem that the invention is trying to solve]

However, in the method of forming a phase shift type diffraction grating, when exposing the diffraction grating to a resist using interference light, a phase shift layer with a controlled film thickness must be patterned, and a complicated element formation process is required. was.

In addition, in order to accurately set the amount of phase shift, it is necessary to accurately predict the change in the propagation constant due to changes in the shape of the waveguide. This required advanced simulation technology.

[Means to solve the problem]

The present invention shifts the phase of light propagating within a laser with respect to a diffraction grating formed in a - shape by bending the stripe structure forming the laser.

[For production]

Since it is only necessary to change the mask pattern in the photolithography process, a phase-shift type DFB laser can be manufactured without performing a complicated process for manufacturing a phase-shift type diffraction grating as in the conventional example.

Further, by changing the stripe length of the bent portion, the amount of phase shift can be easily adjusted.

〔Example〕

The present invention will be explained below using examples.

FIG. 1 shows a first embodiment of the present invention, in which a striped resonator forming a semiconductor laser is bent near the center to shift the phase of the laser beam with respect to the diffraction grating.

1 is an n-type InP substrate, and after coating the entire surface with resist, a first-order diffraction grating pattern with a pitch of 240 OA is imprinted using a two-beam interference method using a HeCd laser beam with a wavelength of 325 nm. Then )lBr−)IN<)
Chemical etching is performed using a 3-H20 solution to form a diffraction grating 5. A substrate 1 on which this diffraction grating 5 is carved
On top, a Sn-doped n-1nCiaAsP layer 2, an undoped InGaAsP active layer 3, and a further 1nG
The aAsP buffer layers 4 are sequentially laminated. Next, 4μ
After patterning using a mask having a bent pattern with a width of s, mesa etching is performed to obtain a stripe having a bent part in the center as shown in FIG. Thereafter, a zinc (Zn) doped InP layer 11 is regrown by liquid phase epitaxial method, and an undoped I
An nGaAsP layer 6 is laminated. Next, directly above the striped structure, a 5i02 layer 7 with a window is deposited by CVD.
using this 8102 layer 7 as a mask,
Zn is diffused so as to reach the InP layer 11, and the diffusion regions 10 are formed in a stripe shape. The planar pattern of this diffusion region 10 is shown in FIG. After that, C
An r/Au electrode 8 and a Sn/Au electrode 9 were deposited and alloyed as P-type and n-type electrodes, respectively. Finally, after dividing into chips with a length of about 300 mm by cleavage, an antireflection film made of SiN was deposited on the cleaved surfaces by plasma CVD (not shown), and a phase-shifted DFB laser was fabricated.

Unlike the method of imparting a phase shift to a diffraction grating, this phase-shifted DFB laser does not use a two-layer resist or a phase shift film, and can form a diffraction grating by ordinary interference exposure. Further, since the amount of phase shift can be adjusted only by the length of the bent portion, the design can be easily performed.

In this embodiment, a buried stripe type laser on an InP substrate is used as an example, but the present invention is of course not limited to this, and any semiconductor substrate constituting the laser, such as a GaAs substrate, may be used. First, the laser structure may be either a ridge structure or an internal stripe structure.

〔Effect of the invention〕

As explained above, according to the present invention, a phase-shifted DFB laser can be easily manufactured without using a complicated resist coating process, and the amount of phase shift can also be changed by changing the length of the bent portion of the mask pattern. It can be easily set. Furthermore, by introducing the bent portion, higher-order modes leak at this bent portion, so that stable oscillation of the transverse mode can be achieved. Further, it is possible to easily finely adjust the amount of phase shift of light according to various parameters of the semiconductor laser, and the accuracy and degree of freedom of adjustment can be improved.

[Brief explanation of the drawing]

FIG. 1 is a perspective view including a partial cross section of a phase-shifted DFB laser that is an embodiment of the present invention, FIG. 2 is a diagram showing a plane pattern of the Zn diffusion region in FIG. 1, and FIG. FIG. 3 is a perspective view immediately after forming stripes in the manufacturing process of the illustrated embodiment. DESCRIPTION OF SYMBOLS 1...n-type 1nP substrate, 2...Sn-doped n-type InGaAsP layer, 3...non-doped InGaAsP active layer, 4.=InGaA
sP /< 7 y layer, 5... Diffraction grating, 6... Non-doped InGaAsP layer, 7...510
2 film, 8...Cr/Au electrode, 9...Sn/Au electrode, 10...Zn diffusion region, 11...InP layer. Patent applicant Canon Co., Ltd.

Claims (1)

[Claims] 1) In a distributed feedback semiconductor laser device in which a diffraction grating is disposed within a waveguide or in a portion close to the waveguide constituting a semiconductor laser, the waveguide has a stripe structure, and the stripe structure A semiconductor laser device characterized in that a waveguide having a waveguide has a bent portion in a part thereof. 2) The semiconductor laser device according to claim 1, wherein the length of the bent portion of the waveguide is adjusted such that the phase of light is shifted by π/2 with respect to the diffraction grating at the bent portion of the waveguide.